The present invention relates to an electronic level, and in particular, to an electronic level, which converts a pattern image on a leveling rod to an electric signal by a photoelectric converter and obtains difference of elevation from the electric signal.
A level is a survey instrument for measuring difference of elevation, and it is conventionally a survey instrument for collimating the leveling rod at a survey target point by an operator with a telescope and for visually reading numerical value given on the leveling rod. The electronic level as disclosed in the present invention is a device, which collimates the leveling rod, receives a pattern formed on a photodetection element, calculates the position by converting it to an electric signal, and displays it as a numerical value.
First, description will be given on a measurement principle of an electronic level.
On a leveling rod 1 for an electronic level to be used in association with an electronic level, a first pattern A, a second pattern B, and a third pattern R are repeatedly disposed with equal spacing (p) as shown in FIG. 4. That is, blocks are consecutively disposed, each block having three types of patterns. If the block arranged at the lowest position is defined as 0 block and the patterns are described as R (0), A (0) and B (0), the blocks are repeatedly arranged as R (1), A (1), B (1), R (2), A (2), B (2), . . . . Because all patterns are repeatedly disposed with equal spacing, a signal corresponding to the spacing can be referred to as a reference signal.
For example, the third pattern R has a fixed width with black portion width of 8 mm. In the first pattern A, width of black portion is modulated with maximum modulation width in the range of 10 mm so that 600 mm will be one cycle. In the second pattern B, width of the black portion is modulated with maximum modulation width in the range of 10 mm so that 570 mm will be one cycle.
As described above, in the first pattern A of the leveling rod 1, width of the black portion is modulated so that 600 mm will be one cycle. In the second pattern B of the leveling rod 1, width of the black portion is modulated so that 570 mm will be one cycle. Therefore, the cycle is slightly different between the first pattern A and the second pattern B. At a distance where the least common multiple of the two is reached, similar patterns repeatedly appear. In the above example, similar patterns repeatedly appear at 11400 mm, which is the least common multiple of 600 mm and 570 mm. Accordingly, the phase difference between the signal from the first pattern A and the signal from the second pattern B varies between 0 and 2 xcfx80 in the range of 0 to 11400 mm.
Now, a measurement principle of level height will be described.
First, description will be given on a case of long distance measurement.
When the leveling rod 1 is collimated in an electronic level, a pattern image of the leveling rod 1 is received by a linear sensor. As shown in FIG. 5, a signal from the photodetection element obtained from the linear sensor is processed by Fourier transform, and only the reference signal is picked up and processed by Fourier transform. From the signal processed by Fourier transform, a signal corresponding to the equal spacing pitch p can be obtained. If it is supposed that the phase of the reference signal corresponding to the equal spacing pitch obtained by fast Fourier transform is xcex8, and the phase of address position (m-th bit) of the linear sensor corresponding to the horizontal position H1 is xcex8 m, it is expressed as follows:
H1=(xcex8m/360xc2x0)xc3x97pxe2x80x83xe2x80x83(1) 
That is, the horizontal position H1 can be precisely measured within the equal spacing pitch p (precise measurement).
In order to obtain the horizontal position, it is necessary to obtain the approximate position from the pattern-starting position of the equal spacing pitch p formed on the leveling rod 1. Here, the output signal from the linear sensor is integrated with respect to half-pitch before and after the reference signal (signal corresponding to the equal spacing pitch p). Further, the integration value is weeded out at every three values (product detection), and a signal 1 corresponding to the first pattern A, a signal 2 corresponding to the second pattern B, and a signal 3 corresponding to the third pattern R are obtained as shown in FIG. 6. However, width is not modulated in the third pattern R, and, moreover, maximum modulation width is 10 mm in the first pattern A and the second pattern B, while it is only 8 mm in the third pattern R. The signal 3 corresponding to the third pattern R has almost constant integration value, and it is about 80% of the value of the signal 1 or the signal 2.
The third pattern R, the first pattern A and the second pattern B are repeatedly disposed in a predetermined order. Thus, it is possible to determine which of the third pattern R, the first pattern A or the second pattern B is the signal which has been weeded out.
Further, in order to eliminate the influence of external light such as shade, signals (A-R) and (B-R) are obtained as shown FIG. 7 using the signal corresponding to the third pattern R as the reference.
Next, from the signals (A-R) and (B-R), a set of signals, i.e. R, (A-R) and (B-R), which include address position (m-th bit) of the linear sensor corresponding to horizontal position and include the reference signal, is selected. If the phases of (A-R) and (B-R) are obtained, it is possible to determine at which position of the leveling rod 1 the combination of the first pattern A, the second pattern B, and the third pattern R is located. As a result, approximate level height H2 at the horizontal position can be obtained (crude measurement).
AS described above, the level height H can be obtained as follows: Phase of the reference signal at horizontal position is obtained (precise measurement). Further, it is determined at which position the reference signal corresponding to horizontal position is located according to the pattern-starting position of the leveling rod 1 from the phase difference between the first pattern A and the second pattern B (crude measurement). By aligning and matching the horizontal position H1 obtained by precise measurement with the level height H2 obtained by crude measurement, the level height can be obtained.
Next, description will be given on a case of short distance measurement.
In case of the short distance measurement, much clear images of the first pattern A, the second pattern B, and the third pattern R can be obtained compared with the case where level height is obtained by product detection after Fourier transform in the long distance measurement. Thus, by directly measuring signal width and by determining which block it corresponds to, measurement of high precision can be achieved for short distance.
As described above, it has been practiced on an electronic level that a white/black pattern formed on a collimation surface of the leveling rod is received by the photodetection element and high or low position is detected by discriminating the pattern. In this respect, when the measurement is made at such place as a place with the tree shade in daylight, strong contrast between sunlight and the shade is overlapped on the pattern of the leveling rod, and it is often difficult to judge the pattern on the photodetection element.
It is an object of the present invention to provide an electronic level, in which it is possible to discriminate the pattern even when there is the shade on a pattern surface of the leveling rod of the electronic level.
The electronic level according to the present invention is an electronic level for converting a pattern on a leveling rod to be collimated by photoelectric conversion and for determining difference of elevation, wherein there is provided an irradiation device for irradiating auxiliary survey light to be projected to the leveling rod by pulsed irradiation. The electronic level according to the present invention provides an electronic level as described above, wherein the auxiliary survey light is irradiated in fan-like shape so that a range of the leveling rod to be collimated can be covered. Also, the present invention provides an electronic level as described above, wherein a semiconductor laser is provided as a light source for the irradiation device, and a light beam emitted from the semiconductor laser has a larger beam-spreading angle in vertical direction. Further, the present invention provides an electronic level, wherein there is provided a lens for adjusting the beam-spreading angle to suit visual field of a telescope. Also, the present invention provides an electronic level, wherein a photodetection element for receiving reflection light from the leveling rod is provided and a shutter is arranged on the photodetection element, and the shutter is driven in synchronization with the irradiation device. Further, the present invention provides an electronic level as described above, wherein a photodetection element for receiving reflection light from the leveling rod is provided and the photodetection element receives the light in synchronization with the pulsed irradiation. Also, the present invention provides an electronic level as described above, wherein a retroreflection sheet is attached on a surface with a pattern of the leveling rod under pulsed irradiation. Further, the present invention provides an electronic level as described above, wherein the retroreflection sheet is a colored reflection sheet. By irradiating the auxiliary survey light as pulsed light, influence of the shade on the reflection surface of the leveling rod can be eliminated. By limiting the reflection light entering the photodetection element using the electronic shutter, S/N ratio can be improved.